RPM*is all that is controlled. The fuel control is prevented from delivering any more fuel and this limits engine speed.

"... how will the boat ever be able to produce the max power available to get to MAX RPM UNDER LOAD ?"

The*"speed stop" limits the*travel of the*linkage that*is*produced by centrifugal force*on the governor flyballs.*This controls the travel of the fuel control rod.*

Maybe a good way to describe it is as a "soft" or indirect limit.*When the engine rpm reaches the setpoint for maximum governed rpm or high idle, spring tension*resisting the movement of*the flyballs is at its maximum and no further travel of the fuel*rod is obtained.

When you move the throttle lever all you are doing on the engine is setting the spring tension that the governor seeks to balance, you are not directly moving the fuel*control rod.

If you incorrectly set your speed stop screw to a point at or lower than the fuel stop, then you are correct, you*may never see rated rpm.

The maximum fuel limit is a "hard" limit.*The setscrew physically stops the*control rod from moving any further in the direction of adding fuel.

(Factoid 1: The "cold start" device on the Minimec or Simms governor removes this limit to allow a much larger weight of fuel*to be injected until the flyballs kick*out and pull the control rod back and the normal limit is again in*effect.)

(Factoid 2: The fuel control rod goes to full fuel when the engine stops and does not move back until the engine starts. Pumping the throttle lever does not*add fuel like in a carbureted engine with an accelerator pump.)*

The*difference between these limits is what makes it possible for your engine to adjust to*external forces without the rpm rising or falling and you*having to chase the throttle lever all the time.

*(Factoid 3: The margin between the fuel stop and an engine overload can be eliminated very easily on a boat that is operating very near to its load limit. This can happen on a single engine boat with a "cruise prop"*and a dirty bottom running at full throttle. A twin engine boat*making a sharp turn can also run into this problem. The inboard prop has to work harder and*as its*rpm drops, the fuel delivery*may exceed what the engine can burn.)

Gonna have to go with FF here. This more likely to be a prop issue and not a cooling issue. Also read that the boat has been sitting for 5 years. It is likely not a prop pitch issue but a fouled prop issue. Get a diver down there to take a look and clean her up and then see what you get. The lack of RPM and the black smoke is a dead giveaway. BTW, it is normal to get a slight temp rise when increasing power towards WOT.

Also just FYI, some engines(Volvo in my case) have cooling water bypass....that bypasses a blockage in the raw water cooling circuit. Talk about throwing you a curveball!!!!! Anyway, learned this one the hard way after almost completely rebuilding the cooling system.

Sorry Baker but you are wrong. Insuring the cooling system is up to snuff is imperative for a vessel that has been sitting for 5+ years and probably neglected several years before that. Yes the bottom is likely fouled up too, but a good servicing will insure the engine does not crater as props, growth etc are dealt with.

Sunchaser, you are wrong in categorically denouncing my post as wrong!!!.... I fully agree that you should inspect and service the cooling system of a boat that has been sitting for years. You should do that with a boat that has a perfectly functioning "non-overheating" engine. That wasn't my point(and obviously is yours) But to automatically assume that his particular issue is a cooling system issue when the symptoms of his issue point to overloading...could be a wrong assumption. He gave us the symptoms and asked for our opinions. I gave mine. And I can tell you that you can have a perfectly clean and perfect cooling system and if the prop/engine is overloaded to the point it comes up 400RPMs short of rated RPM, it will cause black smoke and overheat. If he was making max rated RPM and still overheating then we could certainly assume that he is correctly propped and likely no fouling. I will say it again....the SYMPTOMS point to an overloading condition. Now we could certainly have a case where it is both and that could be the case. IOW, my opinion is based upon something other than the temperature gauge. Yours is not!!! Simple as that.

Although you may be correct in jumping to a solution in this case, I prefer to be a bit more methodical, since I do that every day in my job.
That plus the knowledge that many if not most boats out there have tachometers that are not accurate is what would dictate a tach calibration and another sea trial as a first step.
To qualify my comments, I have owned a hand held tach for several years and I "offer" to calibrate friend's boat tachs as a hobby. I even*recalibrated a few boats at an MTOA rendezvous a few years ago (gotta get those pins ya know). *Of the 25 or so that I have done, I would say 80% have been off at least 100 RPM, most more than that. That list of boats by the way, also includes one* 3 month old Mainship* 34 Pilot with Twins. One enigne was 400 off.
(Please do NOT take that as a dig against Mainship....I happen to be an ex owner, and ex local group president, so I spent lots of time aboard Mainships)

As far as cooling system maintenance....most folks ignor until they overheat...I prefer to be very proactive. I realize it has nothing to do with black exhaust smoke but iunless it is up to snuff*the enigne *doesn't stand a chance.

So I am not saying you're wrong or anybody else is right...this is just the way I approcah problems.

Besides....it's a good "excuse" to go buy a hand held tach and a heat gun....LOL

Fully agree with everything you said JL. And I wasn't claiming to be right. I was just defending my position when someone called me out as being flat out wrong....when my opinion was based on "something" and his was based on nothing. *Also, black smoke might confirm that the tach is right. *If it was just overheating and the tach reading, then I would say check the tach. *But the black smoke adds another telltale sign. *To put it yet another way:If you called any diesel shop and said that you were having an overheating issue when you power up and you told them the thing was puking black smoke and that it is not reaching rated RPM, what do you think their first conclusion would be????...it would be the same as mine....again, that is all I am saying.

PS I would never be offended with someone saying something about the make of boat I have(okay maybe.... ). I mean, FF calls Mainships "Dreamkillers"....hahahaha....God love him!!!! * *I realize they are boats and things on boats can go wrong. I have used a handheld phototach thinking my tach was off....turns out it was right and I am underpropped.

You are right Baker, my opinion is baseless and yours is based on ---- smoke. Since we both agree however*that there are at least*two issues, it is up to Mr Higgins to decide which issues he will tackle first.

A surveyor found a thru-hull valve for the raw water intake not opening/closing. The valve handle would operate open/close but the valve stem had snapped and left the valve partially open/closed. The engine under moderate throttle would operate within normal temperature range but once the throttle was pushed, the alarm would quickly follow.

You are right Baker, my opinion is baseless and yours is based on ---- smoke. Since we both agree however*that there are at least*two issues, it is up to Mr Higgins to decide which issues he will tackle first.

I was never caliming to be right.....you are the one that said I was wrong.

My comment was after observing two retired folks attempt to operate in locking thru locks with hanging ropes , and with fixed cables or a sliding post.

The inability to lead secure a line aft thru a hawse hole , meant a 75 year old was hanging on the line pulling his heart out, unsucessfully.

The lack of a simple mid ship cleat , and the factorys refusal to install one on a brand new boat , meant the boat could not ride the wall, , and again the cruising results were dangerous and disasterous , the couples dream ended , the vessel dumped in the dealers lap.

I'm sure the dealer was happy, with a double sale profit.

Besides a pretty and volumeous interior , the purchaser should make sure the boat is usefull for the required tasks. This Mainship was a failure for its owners.

FF, I remember the volley. And I am having a hard time believing they didn't have midship cleats. I have the bottom of the line Mainship....smallest one made, and the midship cleats are at least adequate and actually I would say maybe even oversized. Heck you can see it in my tiny avatar pic so it is big enough to stand out in that small pic. Where is yours???.... Anyway, I was not at all offended by your summation. I thought it was kind of humorous....not for the older couple obviously. Next time I see any newer Mainship I will take note ref the midship cleat.

my diesel mechanic (he is very good, factory trained at CAT and the most experienced and best referenced CAT diesel mechanic in my area).

i was discussing same with him, he distinctly said:

a diesel engine reaches its max heatoutput/load/energy right when the black smoke starts.
it means the engine cannot burn anymore diesel so any excess diesel injected into the manifold is exhausted as black smoke..

so if the black smoke appears well below normal "max hp" rpm setting, it would to me indicate that possible the propeller is "over propped" accordingly, possible as FF refers to as a cruise prop.

Rick, are you insinuating that such a cruise prop could take some years off the diesel engine life span?

Just bought boat, it's been sitting for about four years.* It has a LF120; starts great.* Temp guage stays around 180 all the way up to around 1600 or so RPM.* If I try 1800-2000* the temp goes to 200+ quick.* Now, after reading the post about 3 vs. 4 blade props I'm thinking the prop may be the trouble; 4 blade.* BUT, the oringinal owner (passed away) was an engineer, loved his boat, an had four props (two 3s & two 4s).* The boat; '79 41ft, came with a 3 blade on it.* SO, is my problem the engine or prop?* Oh yea, I only tried opening it all the way once; topped out at 2100 RPM with a lot of black smoke.

*Hi - Know I'm late to the party... read a fair portion of entries so far... not seeing what happened to me and dad, feel I should mention my own past with overheating diesel.

Over heating experience:

Spring 1965,*my dad and I*watched/helped a marine mechanic in a*boat yard in*Freeport LI, NY*install a factory new 180 HP SC Perkins into our really cool, wooden, 1951, 38' custom built, raised deck, single screw sport fisher/cruiser.* From day one it got too hot when pushed above 1600 rpm.* From that start and all way the way into*into*1967 we and every mechanic we could find tried to figure it out... nothing worked.* It would run, but*too hot at higher rpm.* The prop was correct.* Finally dad got really pissed-off and read Perkins HQ the riot act.* Perkins finally sent two techs to come on a cruise with all their testing gear.* Outcome - the engine had a "very slight" crack in the head.* Perkins replaced the head and that motor then ran great for years.* Never ran hot again!* So... just for the heck of it... I recommend checking the head carefully. - Good luck! Art